The purpose of this study is to assess the utility of abdominal muscle stimulation in quadriplegics and paraplegics to produce a cough effort. A range of stimulus parameters will be asessed to dtermine optimal stimulus paradigms. Airway pressure and expiratory airflow will be used as indices of cough effectiveness. If successful, spinal cord stimulation may be a useful tool to restore cough and hopefully reduce the incidence of respiratory complications.